Bad people.

What I want to say is:

Does opponent owe me something? No.
But does it cost anything to the opponent to grant an undo? No again.

So if it doesn't cost anything to the opponent, not granting is just being mean on purpose.
Of course they are allowed to.
And I am allowed to blacklist people on the other side.
Which, for instance, I do every time people do not grant me undo.
So this way I can choose which people I want to play with and which not.

how many people are on your block list?

@UnAttimoAlChess

For me chess is about personal responsibility. I, not anyone else is responsible for what I do. I play a bad move, I try to make better moves in future. I mishandle the mouse, I try to handle it better in future. There is nothing wrong in asking people to take responsibility for their choices and to take ownership of their errors. Trying to punish people for not seeing things your way seems a little conceited. That is just my view, but maybe I don't feel entitled and realise there is nothing in the rules of chess which says I must be treated specially.

You know that blocking players doesn't remove them from your queue pool in quick match, right?

It actually does. My friend and I (Almost same rating. Within the same 50 at the time) tested it. I saw a seek that someone he blocked created, but my friend didn't see the seek.

I'm pretty sure that's since you were looking at the list manually. I remember admins said before if you just click quick match you can still get paired with blocked users if they are also quick matching as well.

@Oxytocinblb

Personal responsibility is also choosing wheter to be nice to your opponent or not.
An error is such because it's not done on purpose. So if somebody has problems with placing a piece, and recognizes less than a second after, there is no teaching if you do not grant undo, apart from teaching you that some people care more about a few useless points than to be respected by your opponent.

This is something I learnt for sure.

I only allow takebacks in casual games, I disabled it for rated games. If you play a serious game takebacks are ridiculous.
And how could you tell a mouseslip from a blunder? I already made stupid blunders (chess blindness) that you would assume to be a mouseslip...
And in general: Considering your rating you should play less blitz but more games with a longer time control if you want to improve. You don't learn chess by playing blitz but by taking your time thinking about your next move to play.

@UnAttimoAlChess

The point of "care more about a few useless points" sometimes voiced by people like you, trying to shift the blame for botching a game to the opponent, is annoying.

The one who asks for a takeback and is insulted if he doesn't get one is the one who cares most about useless points. If he didn't care about points, but only about playing out a good game, he'd admit his own responsibility and resign and then ask for a rematch starting from the position prior to the "mouseslip".

THAT would be worthy of respect.

But I have not seen it happening once in my life.
Because you takeback-junkies DO care about points.

@ProfDrHack

My point is still proven.

Allowing a takeback does cost NOTHING to the allower.
From this point, you can split people into two categories:

A) The ones who allow a takeback, since it does cost nothing.
B) The ones who don't, even if it does cost nothing.

Of course in category B are placed all the people who are not good chess players and want to win exploiting a mouseslip or something like that.
Remember, I'm still talking about a people asking a takeback a fraction of second after the move.

If you are better than your opponent, why not allowing a takeback? You'll win anyways.
If you are worse than your opponent, you'll lose anyways.

So, logic wants that not allowing one is simply admitting that you want to exploit a mouseslip.